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Once Rare, Infection by Tick Bites Spreads

A potentially devastating infection caused by tick bites has gained a foothold in the Lower Hudson Valley and in coastal areas of the Northeast, government researchers have found.

The condition, called babesiosis, is a malaria-like illness that results from infection with Babesia microti, a parasite that lives in red blood cells and is carried by deer ticks. Though far less common than Lyme disease, babesiosis can be fatal, particularly in people with compromised immune systems.

Because there is no widely used screening test for babesiosis, its spread poses a particular threat to the blood supply, scientists said. “We are very worried about it and are doing everything in our power to address this,” said Sanjai Kumar, chief of the laboratory of emerging pathogens at the Food and Drug Administration.

According to a recent report by the Centers for Disease Control and Prevention, there were six cases of babesiosis in the Lower Hudson Valley in 2001 and 119 cases in 2008, a 20-fold increase. In areas where Lyme disease is endemic, like coastal Rhode Island, Massachusetts, Connecticut and Long Island, babesiosis also is becoming very common, said Dr. Peter Krause, senior research scientist at the Yale School of Public Health.

In one study of residents of Block Island, R.I., Dr. Krause found babesiosis to be just 25 percent less common than Lyme disease. Babesiosis also is spreading slowly into other regions where it did not exist before, like the Upper Midwest, said Dr. Krause.

Many people who are infected with the parasite have no symptoms at all, while others experience mild to moderate flu-like symptoms that may last for a few days or as long as six months. “But some people get so sick that they wind up hospitalized, put into an intensive care unit, or even dying,” said Dr. Gary Wormser, chief of infectious diseases at Westchester Medical Center in New York.

In states that track the disease, there are an estimated 1,000 reported cases a year, said Dr. Krause, but he and other experts believe this represents a fraction of the people who are infected. In the Block Island study, researchers tested about 70 percent of the islanders and found that about one quarter of adults and half of children who were infected had no symptoms and were therefore not reported. Even people with mild to moderate symptoms may never see a physician. Even if they do, the condition may not be accurately diagnosed.

Experts fear that many undiagnosed patients may be donating blood. Currently, blood banks do not screen for Babesia because the Food and Drug Administration has not licensed a test for this purpose. The only way to screen a patient is by using a questionnaire, which simply asks blood donors if they are infected.

Babesiosis already is the most frequently reported infection transmitted through transfusion in the United States, responsible for at least 12 deaths. In New York City, six transfusion-associated cases of babesiosis were reported in 2009. Infection by this route can be serious: One study found approximately 30 percent of people who were infected by a transfusion died.

Between 1999 and 2007, several infants in Rhode Island developed babesiosis following blood transfusions. The Rhode Island Blood Center has become the first in the country to use an experimental new test to screen blood for the parasite.

Experts urge blood transfusion patients and their doctors to be aware of symptoms of babesiosis, which can occur up to nine weeks after a transfusion.

The symptoms can be vague (there is no tell-tale rash as there may be with Lyme disease) and include fever, sweats, chills, headache, fatigue, and muscle aches and pains. In people who also have Lyme disease, doctors might suspect babesiosis if the symptoms are particularly severe or the antibiotics are not working, said Dr. Krause. A diagnosis can be confirmed through blood testing.

Infants and adults over age 50 are more likely to get moderate to severe symptoms if infected. People at increased risk of complications include patients with compromised immune systems (such as people receiving immunosuppressants), those who’ve had their spleens removed, and those with lymphoma or H.I.V. or who are being treated for cancer.

If not caught and treated early, babesiosis can lead to such complications as kidney, lung or heart failure. The infection can be treated with antimicrobial medications, but people with serious complications are less responsive to the drugs.

Why the parasite is spreading and why it’s spreading more slowly than Lyme disease are not well understood. One theory is that Babesia may be carried primarily in mice, which don’t tend to travel far afield. The bacterium causing Lyme disease, Borrelia burgdorferi, can be carried by birds.

A version of this article appears in print on June 21, 2011, on page D6 of the New York edition with the headline: Once Rare, Infection by Tick Bites Spreads. Order Reprints|Today's Paper|Subscribe